3,968 research outputs found
Marker für die Zulassung von Maispopulationssorten
The genetic resource of adapted German maize landraces is threatened to get lost. Unsolved admission standards at the Federal Office for Plant Varieties are a main obstacle for breeders to use such material. Until now each application for admission has been rejected due to missing homogeneity. Therefore, population specific marker alleles should be developed and deposited at the Federal Office for Plant Varieties as further selection criteria. A first step is the development of markers for phenotypic apparent traits. We developed three markers for red and white cob glume color and used them for selection of two maize populations. The next step would be the development of non-genic markers. Although these markers have no phenotypic effects they also do not influence yield or other physiological important traits
Landau mapping and Fermi liquid parameters of the 2D t-J model
We study the momentum distribution function n(k) in the 2D t-J model on small
clusters by exact diagonalization. We show that n(k) can be decomposed
systematically into two components with Bosonic and Fermionic doping
dependence. The Bosonic component originates from the incoherent motion of
holes and has no significance for the low energy physics. For the Fermionic
component we exlicitely perform the one-to-one Landau mapping between the low
lying eigenstates of the t-J model clusters and those of an equivalent system
of spin-1/2 quasiparticles. This mapping allows to extract the quasiparticle
dispersion, statistics, and Landau parameters. The results show conclusively
that the 2D t-J model for small doping is a Fermi liquid with a `small' Fermi
surface and a moderately strong attractive interaction between the
quasiparticles.Comment: Revtex file, 5 pages with 5 embedded eps-files, hardcopies of figures
(or the entire manuscript) can be obtained by e-mail request to:
[email protected]
Inverse photoemission in strongly correlated electron systems
Based on exact results for small clusters of 2D t-J model we demonstrate the
existence of several distinct `channels' in its inverse photoemission (IPES)
spectrum. Hole-like quasiparticles can either be annihilated completely, or
leave behind a variable number of spin excitations, which formed the `dressing
cloud' of the annihilated hole. In the physical parameter regime the latter
processes carry the bulk of IPES weight and although the Fermi surface takes
the form of hole pockets, the distribution of spectal weight including these
`magnon-bands' in the IPES spectrum is reminiscent of free electrons. The
emerging scenario for Fermiology and spectral weight distribution is shown to
be consistent with photoemission, inverse photemission and de Haas--van Alphen
experiments on cuprate superconductors.Comment: Revtex file, 4 PRB pages + three figures appended as uu-encoded
postscript. Hardcopies of figures (or the entire manuscript) can also be
obtained by e-mail request to: [email protected]
Anomalous Spin and Charge Dynamics of the 2D t-J Model at low doping
We present an exact diagonalization study of the dynamical spin and density
correlation function of the 2D t-J model for hole doping < 25%. Both
correlation functions show a remarkably regular, but completely different
scaling behaviour with both hole concentration and parameter values: the
density correlation function is consistent with that of bosons corresponding to
the doped holes and condensed into the lowest state of the noninteracting band
of width 8t, the spin correlation function is consistent with Fermions in a
band of width J. We show that the spin bag picture gives a natural explanation
for this unusual behaviour.Comment: Revtex-file, 4 PRB pages + 5 figures attached as uu-encoded ps-files
Hardcopies of figures (or the entire manuscript) can also be obtained by
e-mailing to: [email protected]
Entwicklung von Populationen bei Mais (Zea mays L.) Selektionseffizienz und Leistungsfähigkeit
Maize is one of the most important crops around the world. Global players in seed production offer more than hundreds of different varieties. All of them are hybrids whereas open pollinated varieties (OPVs) are rare or extinct. In Germany (and many other European countries) no new OPVs are registered; efforts to do so failed in the past. The main advantage of OPVs is their phenotypic and genetic heterogeneity and thus their ability to adapt to different environmental conditions. This could be of utmost
interest facing the complex challenge of climate change. Populations based on new breeding material were developed and tested in comparison to actual hybrids and
landraces. While the new populations achieved about 80 % of the hybrid yield, landraces failed with only 65 %. The efficiency of selection methods needs to be improved
Intentions to Use Virtual Worlds for Education
Virtual worlds are becoming increasingly sophisticated, showing potential as an effective platform for a variety of collaborative activities, including learning. This study examines students’ intentions to use the virtual world Second Life (SL) for education, and explores factors associated with their intentions. Based on the Technology Acceptance Model (TAM) and extended factors, a research model is proposed. The model is tested through a survey administered to business school students who participated in Second Life in upper level MIS courses. Results suggest that perceived ease of use affects user’s intention to adopt SL through perceived usefulness. Computer self-efficacy and computer playfulness are also significant antecedents to perceived ease of use of virtual worlds. Implications for educators are presented
The Transformation of AT&T’s Enterprise Network Systems Group to Avaya: Enabling the Virtual Corporation through Reengineering and Enterprise Resource Planning
This case discusses the management and control of a large enterprise-wide implementation of an ERP system while the business model and corporate culture were shaping and being shaped by that implementation. In 1995, the Enterprise Networks Systems business unit of AT&T faced a triad of problems caused by its legacy IT infrastructure, including the lack of timely, accurate financial and operating data, looming Y2K issues and systems capacity issues that were beginning to limit growth. A business plan for change was developed and approved. A project team was assembled to replace 25 years of legacy systems architecture (400+ systems) with a new enterprise systems architecture. The team was to act as change agent by supplanting a myriad of business processes and people practices that were seen as impediments to future growth and profitability. This case describes the design, development and deployment of one of the largest ERP implementations. The project required the implementation of standardized business processes and people practices for 30,000+ associates globally while minimizing the impacts on 1.3 million customers and on shareholders. Simultaneously, upper management set out on a strategy of creating a virtual business by outsourcing major business functions, including IT, Manufacturing and Distribution, and major parts of the sales and service operations. Other major events included the spin-offs of Lucent Technologies and Avaya
Dynamics of an SO(5) symmetric ladder model
We discuss properties of an exactly SO(5) symmetric ladder model. In the
strong coupling limit we demonstrate how the SO(3)-symmetric description of
spin ladders in terms of bond Bosons can be upgraded to an SO(5)-symmetric
bond-Boson model, which provides a particularly simple example for the concept
of SO(5) symmetry. Based on this representation we show that antiferro-
magnetism on one hand and superconductivity on the other hand can be understood
as condensation of either magnetic or charged Bosons into an RVB vacuum. We
identify exact eigenstates of a finite cluster with general multiplets of the
SO(5) group, and present numerical results for the single particle spectra and
spin/charge correlation functions of the SO(5)-symmetric model and identify
`fingerprints' of SO(5) symmetry in these. In particluar we show that SO(5)
symmetry implies a `generalized rigid band behavior' of the photoemission
spectrum, i.e. spectra for the doped case are rigorously identical to spectra
for spin-polarized states at half-filling. We discuss the problem of adiabatic
continuity between the SO(5) symmetric ladder and the actual t-J ladder and
demonstrate the feasibility of a `Landau mapping' between the two models.Comment: Revtex-file, 16 pages with 15 eps-figures. Hardcopies of Figures (or
the entire manuscript) obtainable by e-mail request to
[email protected]
Dynamics of spin ladders
We derive an approximate theory for Heisenberg spin ladders with two legs by
mapping the spin dynamics onto the problem of hard-core `bond-Bosons'. The
parameters of the Bosonic Hamiltonian are obtained by matching anomalous
Green's functions to Lanczos results and we find evidence for a strong
renormalization due to quantum fluctuations. Various dynamical spin correlation
functions are calculated and found to be in good agreement with Lanczos
results. We then enlarge the effective Hamiltonian to describe the coupling of
the bond-Bosons to a single hole injected into the system and treat the
hole-dynamics within the `rainbow-diagram' approximation by Schmidt-Rink et.
al. Theoretical predictions for the single hole spectral function are obtained
and found to be in good agreement with Lanczos results.Comment: RevTex-file, 10 PRB pages with 7 eps files. Hardcopies of figures (or
the entire manuscript) can be obtained by e-mail request to:
[email protected]
A Logic Programming Approach to Predict Effective Compiler Settings for Embedded Software
AbstractThis paper introduces a new logic-based method for optimising the selection of compiler flags on embedded architectures. In particular, we use Inductive Logic Programming (ILP) to learn logical rules that relate effective compiler flags to specific program features. Unlike earlier work, we aim to infer human-readable rules and we seek to develop a relational first-order approach which automatically discovers relevant features rather than relying on a vector of predetermined attributes. To this end we generated a data set by measuring execution times of 60 benchmarks on an embedded system development board and we developed an ILP prototype which outperforms the current state-of-the-art learning approach in 34 of the 60 benchmarks. Finally, we combined the strengths of the current state of the art and our ILP method in a hybrid approach which reduced execution times by an average of 8% and up to 50% in some cases.</jats:p
- …